feat: Sign bounce messages

[j-g00da]

Closes #873

[missytake]

I don't think this approach would work, see my comment. In any case, this PR needs a test.

[missytake]

@j-g00da in the spirit of clean-up april, what's the status of this PR?

[j-g00da]

@j-g00da in the spirit of clean-up april, what's the status of this PR?

CI fails because ci-chatmail runs old filtermail version, it has to be upgraded. Other than that this is ready.

[missytake]

CI fails because ci-chatmail runs old filtermail version, it has to be upgraded. Other than that this is ready.

I upgraded ci-chatmail.testrun.org to main :) weirdly, I can't restart the failed CI jobs, maybe you can rebase on main to re-trigger the CI?

[j-g00da]

staging2.testrun.org works, but staging-ipv4.testrun.org can't authenticate, is the key missing?

[missytake]

staging2.testrun.org works, but staging-ipv4.testrun.org can't authenticate, is the key missing?

ah yes, it is - it runs the tests with --ssh-host @local, and only the github runner has the key. You need to forward the github runner's SSH agent to the VPS, so it can connect to ci-chatmail.testrun.org. Or maybe generate an SSH key for each run, and copy it on the VPS/ci-chatmail.testrun.org before testing, that's better security-wise.

[j-g00da]

I wonder if this will require further changes after #917